1. Field of the Invention
The present invention relates to a pneumatic tire, and in particular, it relates to a pneumatic tire in which a sipe is formed in a land part of a tread surface.
2. Description of the Related Art
Conventionally, in tires in which a sipe is formed in a land part of a tread surface, there have been proposed various sipe configurations for the purposes of enhancing drainage properties and enhancing a wear performance.
For example, JP-A-2006-36102 discloses a sipe configuration in which a wide part for enlarging a groove width from a central part to a bottom part in a depth direction of the sipe is provided, and the wide part is terminated in a position coming inward from the both end parts of the sipe. According to this, for example, in studless tires, adequate collapse of a land part is generated from the beginning of wear to the end of wear, thereby exerting a good edge effect.
JP-A-2005-247105 discloses a sipe configuration in which not only a first wide part extending from a tread surface and terminating on the halfway to a sipe bottom part is provided in a part in a sipe length direction, but a second wide part extending from a position on the way of a sipe depth direction toward the sipe bottom part in a different position in the sipe length direction. According to this, for example, in studless tires, closing of the sipe is suppressed, and an edge effect and a drainage effect are secured.
JP-A-2009-51309 discloses a sipe configuration in which plural wide parts extending over the whole of a sipe length direction are stacked and provided in a sipe depth direction such that the width becomes wider in the sipe depth direction. According to this, for example, in studless tires, the sipe width becomes large with the progress of wear, thereby lowering the rigidity of a land part, so that an edge effect and a water removing effect are secured.
JP-A-11-151913 discloses a configuration in which not only sipes are formed in a narrow groove part on the side of a tread surface and in a thick groove part on the side of a bottom part, but a boundary line therebetween is inclined in a sipe length direction. According to this, it is described that a lowering of a wet performance is suppressed while suppressing an increase of a noise performance to the end of wear.